Ingest Historical Stats

Ingest biomech historical stat rows.

Player resolution: if a row uses player.alias for a pitcher that does not yet exist in player_info, this endpoint will bootstrap the row with team_id=NULL (no team binding is available at this stage). Callers should establish player_info first — either via POST /biomech/sessions (which can resolve team_id from the session's team_id field) or by pre-creating rosters — to avoid teamless pitcher records.